Two groups of patients with speech dyspraxia 15 years following penetrating head injury were compared on acoustic measures of the temporal organization of their speech during tasks requiring rate and stress changes. One group had a residual non-fluent aphasia with speech dyspraxia while the other had normal language functioning and dyspraxia. Although speech rate was significantly slowed in both groups, only those with a co-existing language disorder did not maintain a normal temporal organization of their speech during rate and stress changes. Much of speech production research has employed nonsense syllables which can be phonetically controlled. Ongoing experiments are examining whether the regularity of production (speech invariance) and speech planning differs between highly familiar and unfamiliar words and nonsense syllables. These experiments involve normal controls, Parkinson patients and chronic adult stutterers. The development of a classification system for chronic adult stutterers has been initiated. Our aim is to relate the different speech characteristics seen in this group to a subclassification system which is predictive of treatment response. Studies of the pathophysiology of oral-lingual dyskinesia before and after treatment are continuing.